This invention relates to a system for testing the attenuation of fiber optic cables. While the invention is described with particular reference to its use with aircraft systems, whose skilled in the art will recognize the wider applicability of the inventive principles disclosed hereinafter.
Fiber optic cables are finding increased application in a variety of products, including aircraft control systems. They are useful in aircraft, for example, because the cables are light weight, because the cables do not require special shielding in that cross coupling between adjacent cables or between other electromagnectic sources and a particular cable does not affect data transmission, and because the cables still retain the flexibility and pliability of more conventional electrical conductors. For all their above-described advantages, however, fiber optic cables are difficult to test reliably to ensure that the cable's integrity is intact or that its performance has not been subject to degradation in use. This difficulty is particularly true with respect to aircraft flight systems, where access to the cables often is restricted physically.
The invention disclosed hereinafter provides a relatively simple and effective device for testing the attenuation of a fiber optic conductor. In the preferred form of the invention, a separate transmitter and receiver are provided which are operatively connected at opposite ends of the cable under test. The transmitter is adapted to provide a test signal to the fiber optic conductor. A timing pulse also is generated and combined with the test signal for transmission. The amplitude of the timing pulse is higher than the test signal so that any cable whose attenuation is within the test range is automatically within the range of timing pulse recovery. The receiver separates the timing pulse from the test pulse and utilizes the timing pulse to demodulate the test signal to provide a DC level voltage proportional to the amplitude of the signal wave transmitted through the cable. This DC voltage is compared with a reference signal and any differences are displayed as attenuation to the receiver operator. Because the reference signals are generated in the respective transmitter and receiver of the system, no physical connection, except the cable under test, is required between the transmitter and the receiver. Alternatively, the transmitted signal may be passed both through the cable under test and a reference cable, and then compared in the receiver to establish the attenuation in the fiber optic cable under test.
One of the objects of this invention is to provide a system for testing the transmission capabilities of fiber optic conductors.
Another object of this invention is to provide a fiber optic conductor test system employing a transmitter and a receiver, which may be separate units interconnected only by the fiber optic conductor under test.
Another object of this invention is to provide a system for testing fiber optic cables in which a test pulse and a timing pulse are transmitted simultaneously through the cable under test.
Another object of this invention is to provide a fiber optic cable testing system in which a receiver is designed to obtain a test signal and a timing pulse through a cable under test, the timing pulse being used to provide a demodulation signal for the test signal.
Other objects of this invention will be apparent to those skilled in the art in light of the following description and accompanying drawings.